1. Field of the Invention
The present invention relates to systems and methods for preventing unauthorized reception of media programs and in particular to a method and apparatus for verifying the contents of a memory storing instructions for granting access to such memory programs.
2. Description of the Related Art
One method to assure the security of the media programs broadcast over such systems is through the use of a conditional access module (CAM) removably coupled to the media program receiver. The media programs are transmitted and received in encrypted form, and a decryption engine disposed in the CAM is used to decrypt such media programs so that they can be presented to the viewer. If the encryption operations in the CAM are compromised, unauthorized access to the media programs may result.
CAMs typically include a microprocessor, a memory storing microprocessor instructions, and an input/output (I/O) module. Most successful attacks on the security of the CAM occur through external, non-invasive attacks against the microprocessor instructions stored in the memory, and occur through the CAM's input/output (I/O) module. Currently, unauthorized reading and/or modification of the memory is detected by using the microprocessor to read the contents of the memory, generate a checksum, and compare that checksum to an expected checksum. However, since the microprocessor reads the memory, the attacker may gain access to the memory through some form of external attack, using the microprocessor and the I/O module.
What is needed is a method and apparatus for verifying the contents of the CAM memory which is immune to attacks through the I/O module and the microprocessor. The present invention satisfies that need.